The long term goal of this project is to understand basic mechanisms of cell death. Many age-related degenerative conditions are related to cellular attrition. This decline is particularly acute in the nervous system, which has a severely restricted capacity for the addition of new cells; cell death is a significant element in many neurodegenerative diseases. A rational therapy to reduce or eliminate cell death will require an understanding of how cells die. Although accumulating evidence points to a "suicide program" which cells turn on if deprived of special signals, the broadest outlines of this program are still a matter of conjecture. The work proposed here aims to begin a cellular and mutational analysis of cell death in the developing Drosophila retina. The compound eye of the fly is a sensitive pattern amplifier of a simple neural module, the unit eye, or ommatidium. Each ommatidium is an exact repeat of a stereotyped unit crystal. Ommatidial development is well characterized at the cellular level, and cell death plays a key role in eliminating surplus cells from the eye lattice. A roughened lattice results if these extra cells are not eliminated, and allows a rapid and powerful screen for mutations that disable normal cell death. The baseline of cell death in normal eyes will be accurately mapped using a variety of methods, including quantitative light and electron microscopy, indicators for intracellular free calcium, and specially constructed genetic transformants. Rough-eyed mutants will be screened to select eyes with surplus cells and these will be examined to select candidates defective in normal cell death. Putative "cell death" mutants will be compared closely to the normal baseline. Genetic methods will be used to determine the site of action of the gene product. Additional alleles of the gene will be generated, particularly with a view to future molecular characterization of the selected gene(s). Many fundamental cellular mechanisms were established before arthropods and chordates diverged, and it is reasonable to expect that a process as basic as cell death will show strong parallels in the two groups. The ability to bring to bear a combination of cellular, genetic and molecular methods in the Drosophila eye has proved useful in exploring how cell fates are specified during development, and it promises to be informative regarding the machinery of the ultimate fate.